Reflexes

Pupil to Pupil

For grades 3-12

Make the lights
in the room dim. After a few minutes, look at the eyes of another person
and note the size of the pupil (the black center spot in the middle of
the eye). Turn on the bright room lights. Check the size of the pupil again.
The pupils should now be smaller. This is the pupillary
response: it "automatically" keeps out excessive light
that may damage the eye.

Materials:

Just a room you can make dim

Jump to It!

For grades K-12

Here's a quick demonstration of reflexes...first talk about how the
brain and the rest of the nervous system controls movement. Then, suddenly
slam a book on a table to create a loud noise. Ask the class and count
the number of students who:

Twitched

Moved their heads

Blinked their eyes

Put their hands up

Screamed

Reflexes are used to protect the body without us having to think about
what is happening...reflexes get us away from objects that might hurt us,
before they hurt us. For example, if you put your hand on a hot stove,
your immediately remove your hand BEFORE the message, "Hey, my hand
is on a hot, burning stove", gets to your brain.

Materials:

A large book or other heavy object to make a noise

Knee Jerk Reflex (Patellar Reflex)

For grades 6-12

The knee jerk reflex is one we are are
familiar with...the doctor hits your knee and your leg kicks out. Try it!
Have a partner sit with his or her legs crossed so that his leg can swing
freely. Hit his leg just below the knee with the side of your hand. DO
NOT USE A HAMMER!!!! The leg will kick out immediately (if you hit the
right place).

The
knee jerk reflex (seen in the figure to the right) is called a monosynaptic
reflex. This means that there is only 1 synapse in the neural circuit
needed to complete the reflex. It only takes about 50 milliseconds of time
between the tap and the start of the leg kick...that is fast. The tap below
the knee causes the thigh muscle to stretch. Information is sent to the
spinal cord. After one synapse in the ventral horn of the spinal cord,
the information is sent back out to the muscle...and there you have the
reflex.

Think Fast!

For grades 3-9

Our built-in reflexes
really do protect us. Another demonstration of these built-in capabilites
is the blink reflex. Have a student stand
behind a see-through barrier like a window or a wire screen. Throw a cotton
ball at the person. Did he blink? Probably. This is the blink reflex and
serves to protect our eyes from damage.

Materials:

Cotton balls (or rolled-up paper towels)

A transparent barrier (a wire screen, plastic or glass window)

How Fast are You?

For grades K-12

Unlike the other
activities on this reflex page, this project does not test a simple reflex.
Rather, this activity is designed to measure your response time to something
that you see.

Get a ruler (or a yardstick or candy bar). Hold the ruler near the
end (highest number) and let it hang down. Have another person put his
or her hand at the bottom of the ruler and have them ready to grab the
ruler (however, they should not be touching the ruler). Tell the other
person that you will drop the ruler sometime within the next 5 seconds
and that they are supposed to catch the ruler as fast as they can after
it is dropped. Record the level (inches or centimeters) at which they catch
the ruler (you can convert the distance into reaction time with the chart
below). Test the same person 3 to 5 times (vary the time of dropping the
ruler within the 5 second "drop-zone" so the other person cannot
guess when you will drop the ruler).

Here is a table to convert the distance on the ruler to reaction time.
Remember that there are 1,000 milliseconds (ms) in 1 second.

Distance of catch

Reaction Time
(in seconds)

2 in (~5 cm)

0.10 sec (100 ms)

4 in (~10 cm)

0.14 sec (140 ms)

6 in (~15 cm)

0.17 sec (170 ms)

8 in (~20 cm)

0.20 sec (200 ms)

10 in (~25.5 cm)

0.23 sec (230 ms)

12 in (~30.5 cm)

0.25 sec (250 ms)

17 in (~43 cm)

0.30 sec (300 ms)

24 in (~61 cm)

0.35 sec (350 ms)

31 in (~79 cm)

0.40 sec (400 ms)

39 in (~99 cm)

0.45 sec (450 ms)

48 in (~123 cm)

0.50 sec (500 ms)

69 in (~175 cm)

0.60 sec (600 ms)

This reaction time experiment required visual information (the movement
of the ruler) to travel to your brain. Then your brain sent a motor command
("grab that falling ruler") to the
muscles of your arm and hand. If all went well, you successfully caught
the ruler!!

Questions and Comparisons

Test the whole class. Who
is fastest?

Compare boys vs. girls. On average,
are the boys or girls faster?

Compare different ages.
Who is fastest?...the older students or younger students?

Compare the scores after
practice. Does reaction time improve with practice?

Compare kids' scores vs.
parents' scores. Who is faster?

Test the whole school!!

Test the whole city!!................you
get the idea.

Materials:

Ruler or yardstick or long candy bar (give the candy bar to the person
with the fastest reaction time)